The present invention relates generally to the propagation and emission of light in optical fibers and more particularly to methods for controlling illumination in light emitting optical waveguides and to waveguides in which controlled illumination occurs.
Optical fibers are being used with increasing regularity in sensor applications as described, for example, in U.S. Pat. No. 4,834,496 issued May 30, 1989 to Lee L. Blyler, Jr., et al. which discloses distributed fiber optic chemical sensors. Such sensors comprise an optical fiber with a core and a cladding that is permeable. The cladding, or a coating on the cladding, includes a composition, the optical properties of which are altered in the presence of a material to be detected. The light (i.e. the wavelength or the intensity of the light) transmitted through the core of the fiber is a function of the change in optical properties caused by the interaction of a composition included in the permeable cladding or coating with the material to be detected. The change in optical properties may comprise (for example) a change in the index of refraction (or indices of refraction differential), or an increase or decrease in the optical absorbance or fluorescence of the composition.
The above noted copending application describes techniques for controlling the power dissipated in an optical fiber in order, for example, to provide a loss-compensated distributed sensor where the sensitivity of the fiber is linear throughout its length.
Typically, an optical fiber, having a core and a surrounding cladding, is designed to transmit and contain light within the fiber core. Light escaping from the core is considered an undesirable characteristic, as it creates a loss of power or the ability to carry information. In other applications, as in the copending application referred to above, light which travels out of the core through the cladding can be exploited for sensor applications.
The present invention refers to that discovery that an optical fiber can be designed with light emission properties, suitable for illumination, in a manner to produce light distributed along the fiber length or in a pattern of discrete segments at intervals along the fiber length.
The present invention describes methods for controlled light emission in an optical fiber or optical waveguide assembly to produce specified illumination patterns. Such patterns include distribution along a fiber length, or a selected pattern of discrete segments of distributed light at intervals along the fiber length. A pattern along a fiber length may be, for example, uniform or may vary according to a selected variation.
The invention is based on the realization that the characteristics of light transmitted through an optical fiber can be modified by changing, for example, the refractive index ratio and/or the absorption and scattering coefficients of the core and cladding of the fiber to control the fiber""s light emission characteristics to allow the emission of light for illumination purposes.
In one embodiment of the invention, light emission is controlled by changing the core/cladding refractive index differential, also referred to as the ratio, along the length of a fiber and by inducing light scattering centers within the fiber core.
In another embodiment of the invention, distinctive light patterns are created along the fiber by introducing scattering centers such as reflective or refractive light scattering particles or voids so that light is emitted only in selected length segments.
In another embodiment of the invention, light emission along the length of a fiber is controlled by changing the core/cladding refractive index differential and by deforming the normally smooth surface texture of the fiber core/cladding boundary to promote radial light leakage.
In another embodiment of the invention, the diameter of the fiber core is changed along the length of the fiber and the core is interspersed with refractive or reflective light scattering particles or voids to promote light emission.
In another embodiment of the invention, the fiber is fabricated with a decreasing absorption coefficient core or cladding and a textured core/cladding boundary to promote light emission.
In another embodiment of the invention, the diameter of the fiber core is increased along the length of the fiber and the core/cladding boundary is texturized to promote light emission.
In another embodiment of the invention, the fiber is fabricated with a decreasing absorption coefficient core or cladding and the core is interspersed with refractive or reflective light scattering particles to promote light emission.
In another embodiment of the invention, the fiber includes a reflective surface to backscatter light emitted longitudinally from the fiber.
In another embodiment of the invention the core and/or cladding of an optical fiber is mechanically scribed in a variable pitch spiral configuration to promote light emission. The pitch can be selected to provide uniform light emission along the length of the fiber.
In another embodiment of the invention, the refractive index of a glass or plastic slab is incrementally changed and scattering centers are introduced to produce an illumination plate.
In another embodiment of the invention, an illumination fiber is imbedded in a glass or plastic slab having a varying refractive index to produce an illumination plate.
In another embodiment of the invention, a slab type core with distributed light scattering centers is sandwiched between two cladding layers having varying refractive indices to provide a bi-directional light emission plate.
In another embodiment of the invention, illuminator sheets with different colored light sources are arranged in a multi-color array.
In another embodiment of the invention, multiple light-emitting fibers are distributed along a planar sheet to provide an illuminator panel.
In another embodiment of the invention, integrated optic waveguides are distributed along a planar sheet to provide an illuminator panel.
These and other embodiments of the invention will become apparent in the following description.